Animal caging and biological storage systems

ABSTRACT

A novel microisolation container for laboratory animals or other species includes a rectangular, transparent base containing an intake port at the lower front end and a detachable top sealingly attached to the base which contains an exhaust port in the end opposite the intake port. The intake and exhaust ports are preferably covered with a filter membrane which excludes airborne contaminants. The interior of the top is contoured to provide a domed sloping ceiling for the container, the lower portion being adjacent the intake or front end of the container and the upper portion being adjacent the exhaust or rear end. Preferred embodiments include a feeder assembly which is supported by perforated supports which serve as shelter for the animals. The front and rear ports, the contoured ceiling and the feeder design aid in the laminar flow of air through the cage. A perforated floor, absorbent insert and disposable waste bag can be included in the base of the cage.

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Applicant's provisionalapplication U.S. Ser. No. 60/071,631, filed Jan. 16, 1997, which isincorporated herein by reference.

FIELD OF INVENTION

[0002] The present invention relates to closed-system caging or storagesystems for animals, biological materials, plants or the like,incorporating intake and exhaust filter membrane ports as barriers tothe movement of contaminants into or out of the isolation containers.Ventilation by convection flow (passive) or mechanical (active) exhaustsystems provide quality contamination-free air to the occupants andhandlers.

BACKGROUND OF THE INVENTION

[0003] As described in Wolfe's U.S. Pat. No. 5,190,879 (filed 1991),millions of laboratory animals have been used every year in experimentalresearch. These animals range from mice to non-human primates. In orderto conduct valid and reliable experiments, researchers must be assuredthat their animals are protected from pathogens and microbialcontaminants that could affect test results and conclusions.

[0004] There are presently at least 1300 research facilities and 223federal agencies registered with the U.S. Department of Agriculture(USDA) that use registered laboratory animals. (Crawford, “A review ofthe animal welfare enforcement report data, 1973-1995,” AWIC Newsletter,Summer 1996) These facilities include institutions, organizations andcorporations such as hospitals, colleges and universities, diagnosticand toxicology laboratories, pharmaceutical companies and biotechnologycompanies. In 1995, these combined organizations used a total of1,395,463 registered animals, of which 333,379 were Guinea pigs and248,402 were hamsters. In addition to these registered facilities, thereare nearly a thousand Institutional Animal Care and use Committees(IACUC) that report to the Public Health Service (PHS), mostly theNational Institutes of Health. Some 90 percent of the animals used atthese institutions are mice and rats, but exact figures for mice andrats are not known, since they are not registered animals. Nevertheless,it is estimated that the United States uses between 15.3 and 18.7million mice and rats a year. (See Mukerjee, “Trends in AnimalResearch,” Scientific American, February 1997, pp. 86-93 and Stephens,“A Current View of Vivisection Animal Research in America,” The Animal'sAgenda, September/October 1996, pp. 20-25.) In Canada, 1.25 million miceand 650,000 rats were reported (by Mukergee, supra) to have been used in1992 for research. These figures exclude permanent breeding populationsat research institutions and commercial suppliers, which are estimatedto number 1.5 million mice and 500,000 rats.

[0005] Many laboratory animals in the past have suffered subclinicalinfections, in which they did not demonstrate any overt signs ofdisease. Because more research is now being conducted at the molecularand microscopic level, these subclinical infections are being discoveredand are invalidating research. Various studies have demonstrated thatcontamination and compromised animal integrity are pervasive problems inthe United States. The loss of biological integrity results insignificant losses in valuable research time and money in laboratoryanimal research.

[0006] Since the conditions of housing and husbandry affect animal andoccupational health and safety as well as data variability, andinfluence an animal's well-being, the present invention relates to abiological barrier/isolator caging system for laboratory animals topermit optimum environmental conditions and animal comfort. Because ofrisks of contamination, biocontainment requirements, DNA hazardousissues, gene transfer technologies disease induction, allergen exposurein the workplace and animal welfare issues, current caging systemtechnologies would appear insufficient to support the modernbiotechnology industry. The objective of the invention is to attainperformance standards such as the exclusion of pathogenic andopportunistic organisms, containment of biological products, hazardousmaterials, allergens and bioaerosols, elimination of intracagecontaminants and control and maintenance of an optimal microenvironment.The invention should also have the effect of improving laboratory animalhousing conditions.

[0007] The health quality of research animals has recently improvedenormously, creating a need for specialized caging equipment. Animalsuppliers around the world have experienced an unprecedented demand fordefined pathogen-free animals, and are now committed to the productionand accessibility of such animals to researchers. The needs forimprovement and technological advancement for efficiently, safely andcomfortably housing laboratory animals arise mainly from contemporaryinterests in pathogen-free, immunocompromised, immunodeficient,transgenic and induced mutant (“knockout”) animals. Transgenictechnologies, which are rapidly expending, provide most of the animalpopulations for modeling molecular biology applications. Transgenicanimals account for the continuous success of modeling mice and rats forhuman diseases, models of disease treatment and prevention and byadvances in knowledge concerning developmental genetics. Also, thedevelopment of new immunodeficient models has seen tremendous advancesin recent years due to the creation of gene targeted models usingknockout technology.

[0008] The number of publications on these subjects has increased from64 for transgenic and one for knockout in 1986 to 1726 and 496,respectively, in 1996, based upon a Medline search. Further projectionsthrough Medline search trends predict that about 2454 papers will bepublished in the year 2001. Estimating the numbers of animals requiredat 200 per report, this means an estimated 500,000 mice will need to bemaintained under proper barrier caging. The pharmaceutical industrypresents new trends in research, resulting in a marked shift from acuteto chronic disease studies. They incorporate the technology of geneticengineering into the traditional medicinal chemistry research process.

[0009] Unfortunately, transgenic animals are very often contaminated or“dirty” animals, because of the lack of proper animal care facilityresources to protect the health of the newly-created animals. Thecurrent scientific advances and opportunities raise complex questionsthat must be addressed by researchers and animal care professionals.These questions include how to manage risks to compromised animals, toresearch personnel and the society at large of animal-to-human diseasetransmission through genetic manipulation, and how and whether toprovide adequate resources for research and breeding applications of thenew mutants. It has been suggested that animals expressing pathogenictransgenes may suffer from unique diseases. In light of the risks oftransmission of disease to the animal users, some mechanism is needed toensure attention to adequate biocontainment and health protection oftransgenics and knockout mutants for minimizing exposure and forcontinued contamination control. Also, it is essential to consider thatinfectious agents, opportunistic organisms, allergens, airbornecontaminants, fomites and environmental factor fluctuations have thepotential to induce animal stress and diseases and variability inresearch or testing data. Animals become more vulnerable to diseases andmore susceptible to human and cross-contamination as we useimmunocompromised and genetically altered mutants.

[0010] Scientists refuse to use animals that are not healthy and caredfor properly. Illness, undue stress or poor living conditions wouldinterfere with obtaining valid, useful results from scientificexperiments using animals. In brief, excellent science requiresexcellent care. The value of the animals used in biomedical research hasincreased substantially with the advent of gene transfer technology. Forinstance, the cost of a single transgenic white mouse could easilyexceed $100,000 when the time and effort required to effect a successfulgene transfer is considered. (Cooper, “Design Considerations forResearch Animal Facilities,” Lab Animal, September 1989, pp. 23-26.)These lines of animals are not only extremely valuable but alsofrequently irreplaceable. Therefore, they need to be provided with thehighest quality environments and protected from cross-contamination. Theliving conditions for such animals must be kept at or near their idealenvironment. Therefore, barriers at cage level must be provided toensure both exclusion and containment in environments appropriate forthe species. Transgenic technology will certainly become more importantin the future, and with the contemporary world harmonization of animalwelfare standards, it is necessary to ensure that the animal's (product)investment is protected. The caging systems of the present inventionwill satisfy scientific expectations.

[0011] These new laboratory technologies require a larger number ofanimal cages to be maintained in the same floor space. The presentinvention provides means of reducing facility construction costs andanimal husbandry-related expenses without jeopardizing the quality ofthe care provided to the animals or the value of the scientific researchconducted. Transgenic colony management is very expensive, especially ata time when animal rights activism is increasing research animal carecosts. As animal purchase and maintenance costs steadily increase whilegrant funds decrease, cost containment of the transgenic colonies usedin research becomes increasingly important. Since labor is the greatestsingle cost, reducing labor is the key to reducing overall costs. Sincespecialized microisolation cages and labor costs are both significant,substantial reduction of caging costs will help to accomodate researchusers. For example, as with long-term testing and the associated risk oflosing a colony, research managers are required to decide whether to usemass air systems and whether they need clean rooms, with their highinstallation costs, to provide high quality animals and avoid possiblelosses of time and data. Installing clean rooms can require expendituresof $400 to $500 per square foot, so the availability of the cagingsystems of the present invention will reduce these costs by offeringprotection similar to a mass air room, but at cage level. The presentinvention also provides a type of automation for changing cages, toeliminate the cost of bedding and bedding-related activities includingbedding ordering, receiving, storage, dispensing, autoclaving, dustremoval, bedding disposal, cage-scraping, bagging, disposal and removalof soiled bedding.

[0012] Many animal pathogens can become airborne or travel on fomitessuch as dust. Therefore, open-system caging operations present a risk ofcontamination. Most research institutions are presently caging mice infilter-top cages (at a cost of about $65 per cage plus $140 forancillary equipment), which have been shown to reduce concentrations ofairborne pathogens as well as allergens, compared with conventionalopen-top cages (which cost about $40 per cage plus $30 for ancillaryequipment). Rodent cages with filter-tops create a contaminant barrierat the cage level. However, they restrict ventilation, prevent heatdissipation and affect the quality of animal research data. Ventilated(positive pressure, open system) cage and rack systems (which cost about$130 per cage plus $150 for ancillary equipment) that protect animalhealth and reduce exposure to airborne contaminants are commerciallyavailable. However, they are expensive and leak pathogens into theworkers' environment. Cage and rack systems that exhaust air through aHEPA filter system before returning it into the room substantiallyreduce the concentration of airborne allergens, but are very expensive(about $200 per cage plus $150 for ancillary equipment). Such cage andrack systems are used in barrier animal facilities, which cost around$400-600 per square foot. Besides increasing the cost of housing micesignificantly, such systems tend to invalidate research data andadversely affect animal well-being. They are still open systems whichleak into the work environment, thus exposing both animals and workersto potential risks of contamination and allergies. In proportionalterms, caging mice in filter-top cages costs approximately 293 percentmore than caging them in open cages. Caging in HEPA ventilated cage andrack systems costs about 400 percent more, while caging inHEPA-ventilated in-and-out cage and rack systems would cost about 500percent more.

[0013] In addition to protecting animals from extraneouscross-contamination, there is a need to isolate laboratory personnelfrom allergens that are indigenous to a species or hazardous agents thatare experiment specific. For example, many technicians and scientistsare troubled by allergic reactions to animal dander. Allergens are alsofound in the urine of mice and rats. There is also the threat ofcontracting contagious diseases that are present in animal studies.Animals may become contaminated at the research facility or in transit,where they are exposed to the outside environment.

[0014] As reported in the Denver Post, Jan. 1, 1998, two researchers atthe Yerkes Regional Primate Research Center of Emory University haverecently been exposed to the hepatitis B virus via contact with cagedresearch monkeys, and the first worker died Dec. 10, 1997. In an erawhen research animals are infected with various virulent diseases,clearly it would be desirable to provide improved protection to researchstaff, which can be accomplished by the caging systems of the presentinvention.

[0015] The current technology (as described in U.S. Pat. No. 5,190,879)for isolating small laboratory animals in research facilities includesfiltered air hoods, filtered air housing units and filtered air rooms.These systems are very expensive and are stationary in nature. There iscurrently a trend towards the use of micro-isolation cages, in whichonly the food, water and bedding have to be changed in a horizontal flowClass 100 air displacement bench or the like. The isolator caging systemuses a standard solid bottom (shoebox) cage equipped with a filter top.The top consists of a polycarbonate frame fitted with a piece of filtermedia. It is made of a spunbonded polyester material known as Reemay™filters that have different particle arrest capabilities. The fabric'sability to pass air is inversely proportional to its particle arrestcapability.

[0016] Cage manufacturers use different types of Reemay filters, but themost current are the 2024, 2033 and 2295. The Reemay 2024 has an 85percent atmospheric dust removal efficiency for particles in the 1 to 5micron range but only a 28 percent efficiency for particles in the 0.3to 1 micron range. The rim at the bottom of the filter top, where itfits over the underlying cage, is made of a lip, forming a junctiondesign similar to that in a Petri dish. (Lipman, “Microenvironmentalconditions in Isolator Cages, An Important Research Variable,” LabAnimal, June, 1992, pp. 23-26.) Despite the large exposed filter surfacearea and the permeability of the filter media, studies have shown thatthe air exchange in isolator cages does not take place through thefilter, but at the junction of the lid with the cage. Additionally, theresults showed that the filter top reduced air exchange rates within thecages to less than one air change per hour (ACH) regardless of the ACHrate provided in the animal room. (Keller et al., “Evaluation ofIntracage Ventilation in Three Animal Caging Systems,” Lab Animal, Vol39, pp. 237-242, 1989) These caging systems clearly impede intracageventilation and can lead to an unhealthy microenvironment.

[0017] Also available are filter tops that are constructed of pressedpulp. The pressed pulp forms a dense mat of wood fibers that acts as adepth filter to block the passage of microbial contaminants.

[0018] There are a variety of gaseous and particulate contaminants thataccumulate in the animal's environment. The sources of this pollutioninclude thermal loads generated by metabolic activity, moisturegenerated from respiration, excrement, and the water source, ammoniagenerated by bacteria from the breakdown of urea found in excrement, andcarbon dioxide generated as a metabolic waste product. These pollutantsall need to be removed or diluted via ventilation or else there is asignificantly poor microenvironmental air quality. As the magnitude ofthe differences between isolator cage macro- and microenvironmentalconditions became apparent, cage manufacturers developed caging systemsthat are supply-coupled or directly ventilated, as opposed to theroom-coupled or passively ventilated systems described above. (Lipman,supra, 1992)

[0019] The use of rodent caging systems that provide individualventilated isolator cages is rapidly increasing. These systems have beenshown to considerably improve the microenvironmental conditions to whichrodents are exposed. Ventilated caging systems have also been shown toenhance containment capability at cage level, reducing the opportunityfor cross-contamination. In general, these systems provide filtered airdirectly into the cage, thereby pressurizing it. The positive pressuredifferentials increase the amount of allergens released into theatmosphere, which may increase the risk of allergies developing inresearch or animal care personnel. Caging systems may be purchased withexhaust systems that scavenge air as it exits from the junction of thecage top and bottom and/or the cage top filter. Because of a junctiondesign similar to that of a Petri dish, no ventilated system is capableof scavenging all the air escaping from the cage. (Tu et al.,“Determination of Air Distribution, Exchange, Velocity and Leakage inThree Individually-Ventilated Rodent Caging Systems,” ContemporaryTopics, Vol. 36, pp. 69-79, 1997) Air leakage and release of intracageair into the room is an important source of airborne contamination.

[0020] The use of laboratory animals in research is increasing rapidly,putting research and testing institutions at ever-increasing risks ofoccupational health litigation. Employee health problems andoccupational hazards caused by animal allergens have become asignificant concern at many research facilities. Laboratory animalallergy (LAA) is an important occupational disease that affects between15 and 44 percent of workers in animal care facilities. (Eggleston,“Death by Dander: Laboratory Animal Allergies in the Workplace,” PRIM &R Meeting, San Diego, Calif., Mar. 17, 1997; Olfert, “Allergies toLaboratory Animals—Aspects of Monitoring and Control,” Lab Animal,February 1993, pp. 32-35) Currently, it is reported that fifty percentof animal-exposed laboratory research personnel exhibit allergies to thelaboratory animals, and three fourths of all institutions withlaboratory animals now have animal-care workers with allergic symptoms.For example, a recent study performed at the Karolininska Institute inSweden revealed that nearly 50 percent of animal-exposed personnelevidenced allergies to lab animals. Up to 73 percent of persons,including scientists and animal-care personnel, with pre-existingallergic conditions such as allergic rhinitis (hay fever) eventuallydevelop allergies to laboratory animals. Ten percent of these personsdevelop occupation-related asthma. Currently in the U.S., approximately35,000 workers and 500,000 scientists have been exposed to laboratoryanimal allergens. These people could be eligible for medical andindemnity compensation. Workers' compensation claims related to animalallergies are estimated at about $50 million for the past three years.Despite these statistics, there appears to be no effort to developclosed-system (leak free) caging and work area technology.

[0021] Personnel who are exposed to animal allergens react in such waysas allergic dermatitis, respiratory allergic diseases and anaphylacticsyndrome. The asthmatic reactions that are associated with the illnessmay be life threatening, and chronic occupational asthma can beassociated with irreversible lung disease. This is an IgE mediatedimmune response to allergenic proteins that are produced by the animalsand become airborne on small respirable particles. Exposure tolaboratory animal fur or dander, saliva, serum or other body tissuesshould be minimized. This is a legitimate biological concern, and yetthere are no technological alternatives. Animal caging with special airfiltration for intake and exhaust, contamination-free environments andgood air quality systems are the most efficient methods of containingsuch respirable particles. The annual costs of LAA illnesses could beenormous, including both medical and disability costs and lostproductivity. By eliminating allergen exposures in the workplace, itwould be possible to improve worker health, maintain animal health andreduce operating costs. The caging systems of the present invention areexpected to meet institutional expectations.

[0022] The lack of control of environmental conditions such astemperature, relative humidity, ventilation rate and illumination at theanimal cage level prevents proper validation of research and testingdata and adversely affects animal well-being. The chilling anddehydration of rodent neonates, hairless and nude strains inmechanically ventilated caging systems have caused animal losses due tohypothermia. Thus, there is a growing need for improved caging systemswhich would safeguard the health of both the laboratory animals andtheir keepers. Furthermore, keeping social animals such as rodentspermanently in barren cages is unacceptble for ethical, professional andscientific reasons. It deters the animals from expressing their normalbehaviors and favors stereotypic behaviors instead. It is thus desirableto provide environmentally enhanced caging systems to improve thewell-being of laboratory animals and the quality of research conductedon them.

[0023] Cages currently used to isolate rodents resemble a Petri dish andhave filter tops. They are known as microbarrier (Allentown CagingEquipment, Inc., Allentown, N.J.) or microisolator (Lab Products, Inc.,Seaford, Del.) cages. These cages have a proven isolation capability,but restrict ventilation to less than one air change per hour, thusproviding poor air quality. These cages still leak airborne contaminantsand allergens into the occupational environment. Regardless of thenumber of air changes per hour in the room, such cages operate the samebecause of the cage top design. Cage ventilation in filter-top cages isdriven by thermal and moisture diffusion through the filter top and byconvection across the cage. There is no other escape for thermalcurrents created by the animals in the cage. Computational fluiddynamics has been used to study filter-top cages in a six-shelf rackwith seven cages per shelf. The thermal currents and cumulative effectof metabolic heat load, moisture and toxic gases across the rack wereevaluated for each of the 42 cages for five racks. An animal room wasset at 66 deg. F., 50% relative humidity and 15 air changes per hourwith a changing station in it. It was discovered that there is a lack ofconsistency from position to position of cages on the same rack andacross the room, depending upon where air diffusers and exhausts arelocated. Nevertheless, depending upon the lower or higher locations ofthe cages on the rack, microenvironmental variations were noted on theorder of 3 deg. F., 10% in relative humidity, 2.256 ppm carbon dioxide,4.8 ppm ammonia and two times less air changes/hour. The heatstratification from accumulated hot and humid air creates a barrierinside the tops of the cages and under each shelf, affecting the thermalcurrents. Even though sufficient chilled air is supplied to the room,the chilled air cannot penetrate the barrier of hot air trapped withinthe cages and under the shelves.

[0024] The caging system is an important factor in the physicalenvironment of laboratory animals, the microenvironment.Microenvironmental conditions lack similarity to animal room conditions,the macroenvironment. Animal Welfare regulations (AWA, Guide) prescriberoom (but not cage) temperature, humidity and ventilation settings aswell as solid bottom cages for microenvironmental animal comfort. Thereare three types of solid-bottom caging systems currently used in animalfacilities. Two types of shoeboxes are room-coupled in a static mode:cages with open tops and cages with filter tops also calledmicroisolator cages. The third type is a shoebox with filter topindividually coupled to blower supply and/or exhaust modules anddistribution plenums on a rack. Solid bottom cages with open topsprovide 10 to 16 air changes per hour (ACH), regardless of the roomventilation (Reeb, C. K. et al., 1997). The thermodynamics of convectionand diffusion from the thermal updraft by the heat load of the micecreate the airflow. The open top cage provides microenvironmentalcomfort but lacks isolation, containment, and enrichment capabilities.With 5-mice residing in a static microisolator cage, the air velocity is0.05 cfm, providing 0.02 air change per hour with 4° C. temperature rise(Riskowski et al., 1996). This static filter-top cage has a filtermembrane, making the airflow independent of room ventilation. The filtertop restricts convection and diffusion thermodynamics with the resultantaccumulations of temperature, humidity, ammonia, and carbon dioxide overtime. The filter-top cage thus provides isolation but lacksmicroenvironmental comfort, containment, and enrichment capabilities(Keller et al., 1989, (Maghirang, R. G., 1995, Memarzadeh, F., 1998,Riskowski et al., 1996, Reeb, C. K. et al., 1997, Serrano, L. J., 1971).Ventilated filter-top cages provide 40 to 100 ACH depending onmanufacturers. Pressurization of the cage by “high-efficiencyparticulate air” (HEPA) filter/blower supply and/or exhaust modules isindependent of room ventilation. Velocities up to 100 fpm (air at 20° C.and moving at 60 linear fpm has a cooling effect approximating 7° C.) inthe cage have been recorded, thus inducing cold stress. The individuallyventilated filter-top cage provides isolation but lacksmicroenvironmental comfort, containment and enrichment capabilities(Huerkamp, M. J. and Lehner, D. M., 1994, Lipman, N. S. et al., 1993,Novak, G., 1997, Tu, H. et al., 1997).

[0025] Since all three types of caging systems are independent of roomventilation settings, air handling systems are designed to conditionmacroenvironment or the human occupied zone only. Air handling or HVAC(heating, ventilation, air, conditioning) systems are the most costlycomponent of any animal facility, often consuming 40 to 50 percent ormore of the construction budget (Hughes and Reynolds, 1995). Applicanthas considered means to create a cost-effective caging system that couldbe room-coupled, function in a static mode, and be coupled to thebuilding HVAC exhaust system.

[0026] Computational fluid dynamics (CFD) is a software analysis tool.It uses equations of the conservation of mass, momentum, and energy,which essentially say, “what goes in must come out” (Hughes andReynolds, 1995). This application describes CFD output used tofacilitate the design process and predict air movement in a new type ofcaging system. Contours, vectors, and particle tracks are examined toadjust microenvironmental comfort. The goal was to meet or exceed allcurrent guidelines and regulations at the cage level, while innovatingin cost-effective and appropriate caging systems.

[0027] Application of CFD has demonstrated that vented filter-cages withclosed-tops can provide 6 to 30 ACH depending on the chosen filtermaterials and the room ventilation settings. The thermodynamics ofconvection, buoyant flow and conservation of mass from the thermalupdraft resulting from the heat load of the mice create the airflow thatis dependent upon room ventilation. This vented closed-system for micecaging is believed to be the only one that will providemicroenvironmental comfort, isolation, containment, and enrichment.Applicant conducted a qualitative and quantitative analysis of airdistribution pattern, velocity, air change per hour, and leakage inthese cages. Also studied were temperature, thermal loads from metabolicactivity; humidity, moisture from respiration, wastes, and water source;ammonia, from bacterial breakdown of urea in excrement; and carbondioxide, as a metabolic waste product, all were monitored over a twoweek period.

[0028] Standardized testing methods for characterizing the design andoperation of ventilated caging systems were used by Tu et al. (1997) todefine and quantify differences in air distribution, exchange, velocity,and leakage in three commercially available systems. These methods arealso published as the National Sanitation Foundation Standard 49 forClass II (Laminar Flow) Biohazard Cabinetry (Ann Arbor, Mich., 1992).The concept is particularly relevant since the driving force for theflow is a result of buoyancy due to temperature gradients. In this case,five mice generate heat loads of 2.0265 Kcal/hr and moisture of 2.5 g ofwater/hr. Use of laminar convection flow to ventilate themicroenvironment through filter membrane would eliminate gaseous buildupand provide good air quality within the enclosure. Therefore, naturalconvection airflow should provide an efficient room-coupled‘closed-system’ method for producing adequate microenvironmentalventilation and efficient microbiological barrier at cage level, i.e.provide product and personnel protection.

[0029] Subsequent to the filing of the above-identified provisionalapplication, a literature search was performed concerning mice caging,particularly relating to room air distribution and the relationshipbetween macro- and microenvironments, effects of ambient temperature ongrowth, and moisture production of mice. The following brief summariesdiscuss pertinent publications.

[0030] The Guide for the Care and Use of Laboratory Animals, Instituteof Laboratory Animal Resources (1996), National Research Council,National Academy Press, pp. 23-55, discusses macro- and microenviromentsfor lab animals, including temperature and humidity conditions and thedetermination of optimal ventilation rates.

[0031] Reeb et al. in “Impact of Room Ventilation Rates on Mouse CageVentilation and Microenvironment,” Contemp. Topics Lab. Anim. Sci.,Vol., 36, pp. 74-79 (1997) present a study of non-pressurized,bonnet-topped mouse cages housing four mice each. The effects of roomventilation rate on various aspects of the microenvironments in thecages were examined, and it was found that increasing the roomventilation rate beyond 5 ACH did not result in significant improvementsin the cage microenvironments.

[0032] Maghirang et al. in “Development of Ventilation Rates and DesignInformation for Laboratory Animal Facilities,” Part I—Field Study,ASHRAE Transactions, Vol. 101, Pt. 2, RP-730 (1995) discussed a surveyof animal facilities and their characteristics. It was found that cageconditions varied widely among cages within the same room and amongsimilar cages in different rooms; Cage type was the most importantfactor that influenced cage conditions and uniformity in cageconditions; and room air exchange rate, air velocity approaching thecage, number of returns and diffusers, and diffuser type did notsignificantly influence cage conditions and uniformity in cageconditions.

[0033] Riskowski et al. in “Development of Ventilation Rates and DesignInformation for Laboratory Animals Facilities,” part 2 —LaboratoryTests, ASHRAE Transactions, Vol. 102, Pt. 2, RP-730 discussed theresults of tests of conditions in animal rooms and within animal cagesat selected locations in the rooms. Conclusions included: Cageconditions varied widely with cage location in a room; Cage type was themost important factor that influenced cage conditions; and Room ACHvalues from 5 to 15 had the same effects on cage conditions, so thehigher room air exchange rates did not provide better conditions for theanimals.

[0034] Perkins et al. reported in “Characterization and Quantificationof Microenvironmental Contaminants in Isolator Cages with a Variety ofContact Bedding,” Contemp. Topics Lab Anim. Sci. Vo. 173, pp. 96-113(1995) the results of studies of isolator-type cages housing mice witheight different contact beddings. The presence of ammonia and otherenvironmental contaminants was studied.

[0035] Choi et al. in “Effect of Population Size on Humidity and AmmoniaLevels in Individually Ventilated Microisolation Rodent Caging,”Contemp. Topics Lab. Anim. Sci., Vol. 33, pp. 77-81 (1994), discuss theeffects of population size on the buildup of ammonia and humidity inindividually-ventilated microisolation cages over time as compared tostatic microisolation cages.

[0036] Hasenau et al. in “Microenvironments in Microisolation CagesUsing BALB/C and CD-1 Mice,” Contemp. Topics Lab. Anim. Sci., Vol. 32(1) pp. 11-16 and 32 (2) pp. 58-61 (1993) report the results of studiesof four different mouse caging systems for microenvironmentaltemperature, humidty and ammonia levels.

[0037] In Sato et al., “Dehumidification of Ventilation Air in a BarrierMaintenance System for Laboratory Animals,” Lab. Anim. Sci., Vol. 39,pp. 448-450 (1989) and Wu et al., “A Forced-Air Ventilation system forRodent Cages,” Lab. Anim. Sci., Vol. 35, pp. 499-504 (1985) it wasreported that ammonia is produced in greater amounts under conditions ofhigh humidity. Desiccation was shown to be helpful in the prevention ofammonia and humidity accumulation.

[0038] Corning et al. in “A Comparison of Rodent Caging Systems Based onMicroenvironmental Parameters.” Lab. Anim. Sci. Vol. 40, pp. 498-508(1991) describe two studies of four different mouse caging systems,evaluating them for microenvironmental temperature, carbon dioxide,relative humidity and ammonia levels. The cages evaluated were filterlid vs. open lid types.

[0039] Serrano reports in “Carbon Dioxide and Ammonia in Mouse Cages:Effect of Cage Covers, Population and Activity,” Lab. Anim. Sci. Vol.21, pp. 75-85 (1971) on a study of the effects of rod, wire-mesh andfibrous filter-type covers on diffusion or convection of gases producedin mouse cages. It was found that filter or mesh covers had majorinfluences on the composition of air in the cages.

[0040] Keller et al. in “An Evaluation of Intra-Cage Ventilation inThree Animal Caging System,” Lab. Anim. Sci. Vol. 39, pp. 237-242 (1989)report on a study of air distribution and air turnover rates inunoccupied shoebox mouse cages, filter-top covered cages and shoeboxmouse cages housed in a flexible film isolator. They concluded thatalthough filter-top covered cages reduce the cage-to-cage transmissionof disease, the poor airflow observed within these cages could lead to abuildup of gaseous pollutants that may adversely affect the animals'health.

[0041] Tu et al. in “Determination of Air Distribution, Exchange,Velocity and Leakage in Three Individually Ventilated Rodent CagingSystems,” Contemp. Topics Lab. Anim. Sci. Vol. 36, pp. 69-73 (1997)report on a study of individually ventilated rodent cages. Theinefficiency of exhaust scavenging from such systems compromises theirsuitability for use with hazardous agents. Also, chilling anddehydration resulting from air velocity can result in animal losses dueto hypothermia.

[0042] Applicant's literature review identified the following importantfactors in controlling the macro- and microenvironments for cagedrodents:

[0043] Genetic heritage and environmentally-influenced biologicalresponses.

[0044] Ventilation in filter top cages does not necessarily increasewith increasing room ventilation air exchange rates.

[0045] Filter tops can significantly affect cage ventilationperformance.

[0046] Cage conditions varied widely with cage location in a room.

[0047] Desiccation was shown to be helpful in the prevention of ammoniaand humidity accumulation.

[0048] Improved cage washing procedures and animal room cleanliness mayreduce the concentrations of bacteria that produce ammonia.

[0049] Bedding type can significantly affect ammonia generation.

[0050] A recent study suggests that groups of five mice display abehavioral and autonomic thermoneutral zone that is similar toindividual mice, including a temperature warmer than standard housingtemperatures. This suggest that groups of mice may experience coldstress under standard housing conditions. Ammonia concentration can bereduced by increasing the supply air temperature.

SUMMARY OF THE INVENTION

[0051] It is an aspect of the present invention to provide a suitable,cost-effective closed-system cage assembly for small mammals such asrodents which prevents the transfer of contaminants to or from thesystem. Preferably, natural convection flow will be used.

[0052] Another aspect of the invention is to provide closed-systemstorage systems for biological materials, plants or the like whichprevent the transfer of contaminants to or from the systems.

[0053] It is a further aspect of the invention to provide means forisolating such animals, in transit as well as in the laboratory, frombacteria, viruses and other pathogenic or potentially pathogenic agents.

[0054] Another aspect of the invention is to provide means forprotecting animals in transit, and those exposed to them, at minimalexpense and effort.

[0055] Still another aspect of the invention is to provide means forprotecting and isolating animals in transit and in the laboratory frompollutants or contaminants while allowing free exchange of gases withoutdeveloping excessive temperatures within the containers.

[0056] Broadly, the present invention encompasses an isolation containercomprising a base which supports a plurality of sides, a top affixed tothe sides forming a micro-isolation container suitable to house a heatload, one of the sides having an intake port with a filter membrane anda second side having an exhaust port with a filter membrane, the exhaustport being located higher relative to the base than the intake port onan opposite side, thereby facilitating a convection based air flow fromthe intake port, across the container, and out the exhaust port.

[0057] Preferably the isolation container has four sides forming arectangle, with the intake and exhaust ports located at opposite ends ona pair of shorter sides, and the inner surface of the top slopes upwardfrom the intake port side to the exhaust port side.

[0058] The present invention includes a rectangular isolation containercomprising a base made of transparent material and having an air intakeport covered with a filter membrane at the front end and a detachabletop sealingly attached to the base. The container has an air exhaustport covered with a filter membrane and located on the rear end of thecontainer, opposite the front end of the base. The interior of the topforms a domed sloping ceiling for the container, with the lower portionlocated adjacent to the intake end and the upper portion being adjacentto the exhaust end. The interior of the top is preferably smooth,nonporous and reflective to aid in the flow of gases through the cage.

[0059] The preferred embodiment of the present invention is a cageshaped like a rectangular box and incorporating ventilation ports in thelower and upper portions, respectively, of opposite ends of the box. Theventilation ports are preferably covered with filter membranes.

[0060] In accordance with the invention, the cage comprises arectangular base made of a transparent material and a detachable top.The base includes a ventilation port in the lower portion of one end(front) surface (the intake port), and the base or top includes asimilar ventilation port in the upper portion of the opposite (back) end(the exhaust port) from the intake port. When assembled, the top andbase are attached in an air-tight manner to prevent any flow of airbetween the cage interior and the outside. The cage is thus a closedsystem which is room-coupled via the intake and exhaust ports and filtermembranes. An optional exhaust nozzle can be attached to the exhaustport. The exterior of the cage is rectangular to facilitate stacking ofthe cages in use. The interior of the top is contoured to provide asloping domed ceiling, with the lower portion adjacent the intake end ofthe cage and the upper portion adjacent the exhaust end. This creates asuitable convection laminar flow of air through the cage, as discussedin detail below.

[0061] Preferably the base incorporates a floor and waste disposalsystem comprising a perforated cage insert and a disposable waste bagattached to a cage bottom liner. The liner is made of absorbent materialtreated to prevent the growth of microorganisms and the generation ofdust. Attached to the liner are support members which support the cageinsert at a suitable level above the liner. A feeder assembly comprisesa slotted V-shaped rack for holding feed and suitable perforatedsupports. Preferably, the supports comprise perforated tubes which canbe used by the occupants for shelter. The tubes can optionally betransparent also. Suitable means are provided for securing the feederassembly in position. Proper design and placement of both the feeder andthe perforated tube supports promote laminar air flow through and acrossthe enclosure toward the exhaust port. The feeder assembly alsopreferably incorporates an attachment point for a water sipper tubeextending from a water bag or bottle which is mounted in a recessedportion of the top at the intake end of the cage. A detachableelastomeric securing and carrying strap is provided to secure the top tothe base.

[0062] Other aspects of this invention will appear from the followingdescription and appended claims, reference being made to theaccompanying drawings forming a part of this specification wherein likereference characters designate corresponding parts in the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

[0063]FIG. 1 is a top perspective view of the assembled cage in thepreferred embodiment;

[0064]FIG. 2 is an end view of the exhaust port or rear end of theassembled cage of FIG. 1;

[0065]FIG. 3 is an end view of the intake port or front end of theassembled cage of FIG. 1;

[0066]FIG. 4 is a longitudinal cross-sectional view taken along line 4-4of FIG. 1;

[0067]FIG. 5 is a perspective exploded view of the cage top;

[0068]FIG. 6 is a perspective exploded view of the cage base;

[0069]FIG. 7 is a sectional detail view of the seal between the top andbase of the assembled cage;

[0070]FIG. 8 is a sectional view of an alternate embodiment of the sealof FIG. 7;

[0071]FIG. 9 is a sectional detail view of the intake and exhaust filtermaterials;

[0072]FIG. 10 is a sectional detail view of an alternate embodiment ofthe filter material of FIG. 9;

[0073]FIG. 11 is a top perspective view of the feeder structure;

[0074]FIG. 12 is a side elevation view of the feeder structure;

[0075]FIG. 13 is an end elevation view of the feeder structure;

[0076]FIG. 14 is a top perspective view of the end cage supportstructure;

[0077]FIG. 15 is a top perspective view of the middle cage supportstructure;

[0078]FIG. 16 is a partial perspective view of an alternate embodimentof the middle cage support of FIG. 15;

[0079]FIG. 17 is a partial perspective view of an alternate embodimentof the cage end support of FIG. 14;

[0080]FIG. 18 is an end view of the middle cage support of FIG. 15;

[0081]FIG. 19 is an end view of the end cage support of FIG. 14;

[0082]FIG. 20 is a top perspective view of the cage support structure;

[0083]FIG. 21 is a diagrammatic view of the laminar air flow through thecage of FIG. 1, without accessory obstructions;

[0084]FIG. 22 is a diagrammatic view of the laminar air flow through thecage of FIG. 1 containing a feeder assembly;

[0085]FIG. 23 is a diagrammatic view of turbulent air flow through aprior art microisolation cage with a filter top only;

[0086]FIG. 24 is a side elevation view of an embodiment of the cagehaving a door in the front end above the intake filter;

[0087]FIG. 25 is a side elevation view of an embodiment of the cagehaving a door in the front end which includes the intake filter;

[0088]FIG. 26 is a side elevation view of an embodiment of the cagehaving a door in the side of the cage top;

[0089]FIG. 27 is a top perspective view of an assembled cage in analternate embodiment;

[0090]FIG. 28 is a top perspective exploded view of the base portion ofthe cage of FIG. 27;

[0091]FIG. 29 is a top perspective view of the top of the cage of FIG.27;

[0092]FIG. 30 is a longitudinal cross sectional view of the cage of FIG.27;

[0093]FIG. 31 is a lateral cross sectional view of the cage of FIG. 27;

[0094]FIG. 32 is a front view of an array of cages mounted upon a cagesupport system of the invention; and

[0095]FIG. 33 is a cross sectional side view of the cage array andsupport system of FIG. 32.

[0096] Before explaining the disclosed embodiment of the presentinvention in detail, it is to be understood that the invention is notlimited in its application to the details of the particular arrangementshown, since the invention is capable of other embodiments. Although thepreferred embodiment is designed for isolating plants and animals,including mammals, reptiles, amphibians, fish and birds, in alternativeembodiments the containers can be used for bacterial, yeast, plant oranimal cell cultures. Also, the terminology used herein is for thepurpose of description and not of limitation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0097] In discussing the cage system of the invention, the top or upperportions, the lower or bottom portions and the front (intake) and rear(exhaust) ends will be used as a frame of reference.

[0098] The caging system of the present invention provides performanceefficiency, reliability, cost-savings and animal comfort. It is a uniqueclosed-system design that promotes laminar convection air flow throughindividual cages and across the storage rack. The caging systems of theinvention assure:

[0099] 1) exclusion of all pathogens by keeping the animals “clean,”free of infectious agents, opportunistic organisms, contaminants andpollutants;

[0100] 2) containment of potential sources of contamination such asgases, particulate matter, allergens and fomites, thus avoidingcross-contamination and occupational health hazards;

[0101] 3) elimination of contaminants from feed, water, bedding/nestingmaterials and waste, thus preventing adverse effects on physiologicaldefects, diseases and data variability; and

[0102] 4) creation of a stable environment appropriate for the labanimals by providing optimal microenvironmental conditions and animalcomfort in a spatially-enhanced and enriched environment.

[0103] In the present invention, a filtered closed-system design withgood air quality coupled with a waste disposal system enhancessanitation, reduces cage changing and cleaning, eliminates the cost ofbedding material and its handling and provides the opportunity todevelop safe procedures for cage changing and waste disposal operations.

[0104] Turning now to the drawings, FIGS. 1 to 6 illustrate a completecage system of the invention. The rectangular cage (2) includes a base(4) of a transparent material. Any suitable transparent material can beused, including glass, but preferably a moldable polymeric material suchas high temperature polycarbonate is used to facilitate molding andsterilization of the finished cage. Such materials will withstandautoclave temperatures of about 275 deg. F. The top (6) is made of thesame or a similar material. Base (4) has an intake port (7) at the frontend which is preferably covered by protective grid (26), secured byclips (28). The grid protects a filter membrane (30), the details ofwhich are discussed below. Base (4) also includes an attachment pin orother device (16) for attaching a combination securing and carryingstrap (10) of an elastomeric material such as rubber or siliconepolymers. FIGS. 2 and 3 show strap (10) in an extended position. Thebase (4) also includes a widened portion and notch (18) to facilitatemounting the cage(s) on a system of shelfless brackets, discussed below.

[0105] The top (6) also contains an exhaust port (19) at the back end ofthe cage, covered by grid (22) which is secured by clips (23) andprotects a filter membrane (24). Brackets (20) are provided forattaching an optional exhaust nozzle (25), described below andillustrated in FIG. 5. The top also includes clips or brackets (14) formounting an information card (27) on the cage. The top surface of top(6) is recessed at the front end (38) to provide space for a flexiblewater bag (12). The edges (5) of top (6) form a level contour tofacilitate stacking of the cages. The water bag has a tube (32) whichpasses sealingly through hole (34) in top surface (38) of the top (6).The tube (32) becomes water sipper tube (36) which is preferablysupported by brackets (40) on feeder structure (42), and provides waterto the resident animals. Alternatively, water sipper tube can beattached directly to feeder structure (42). The water tube also helps tohold the feeder structure in position within the base of the cage. Thewater bag is constructed from a flexible, nonporous polymeric materialsuch as a suitable fluoropolymer. Such materials arechemically-resistant and non-toxic and will not contaminate the water. Asuitable wall thickness is about 5 mils. The bags are sealed on all foursides and have a valve or fitting installed on one wall. Suitablefittings can include an on/off valve which will accept flexible tubingor septum fitting which can be used with a hypodermic needle.

[0106] A protective grid (44) is provided inside the cage top to protectexhaust filter membrane (24) from any scratching or gnawing by theresident animals. The grid can be made of any suitable gnaw-resistantmaterial, including stainless steel or polycarbonate polymers. Topsurface (38) of the cage top forms a sloping, domed ceiling for thecage. By sloping upward from the intake or front end of the cage to theexhaust or rear end, the ceiling encourages thermal air currentsresulting from the body heat of the resident animals to provide alaminar convective air flow from intake to exhaust ports. The domedceiling, which is higher along the centerline than at the edges of thetop, helps to achieve the same effect. The surface of the domed ceilingcan be reflective to improve the flow of gases in the cage.

[0107]FIG. 9 shows a cross section of the filter membrane (30) used forthe intake and exhaust filters. This material is discussed in detailbelow. FIG. 10 illustrates an alternate embodiment in which the membrane(30) is protected on at least one side by protective material (41) suchas wire mesh or the like. This serves to protect the filter membrane(30) from damage in handling or from contact with the resident animals.

[0108] Feeder structure (42), shown in detail in FIGS. 11 to 13,includes a V-shaped rack (43) containing feed slots (46). When stockingthe cage, feed can be placed in the V-rack, either loose or in paperbags which the resident animals can gnaw through. Optionally, a powderedfeed tray and air deflector (45) is provided to retain powdered feed andprevent it from being dislodged or contaminated by air currents. Thefeeder can thus handle either pelleted or powdered feed. The feederstructure base includes two open tubes (48) which form the base supportfor the feeder. These tubes serve a dual purpose in that they affordshelter to submissive animals which may flee more dominant animals, andthe perforations (50) allow the animals to sniff each other and morereadily reach social equilibrium. Preferably the tubes are transparentto facilitate interaction between the animals and observations by theirkeepers. Additionally, the support tubes promote laminar air flow acrossand through the enclosure toward the exhaust port. Brackets (40)position the water sipper tube (36) and help to secure the feeder inplace. Any suitable non-toxic plastic or metal can be used for thefeeder structure, but preferably it is made of nylon, polycarbonate orstainless steel.

[0109] The bottom of the cage base includes several components to meetthe needs of the resident animals and their keepers and users. These areshown in detail in FIG. 6. Perforated cage insert (52) covers the othercomponents and may include an upright portion (41) which protects theintake filter membrane (30) from the animals. The cage insert can bemade of any suitable non-porous material, preferably stainless steel ornylon. The cage insert is perforated to allow waste materials to fall tothe cage bottom liner (54) below. Cage accessories such as feederstructure (42) and furniture can also be attached to the insert via theperforations. The cage bottom liner is formed of an absorbent materialsuch as paper, wood fibre or the like and is designed to rapidly absorbmoisture from waste materials from the bottom up. The non-contactabsorbent liner material can be impregnated with particles of zeolites,non-zeolitic molecular sieves or the like to deodorize and absorbmoisture and gas molecules. The liner material is preferably impregnatedwith an antibiotic (e.g. streptonycin, penicillin, or sulfa drugs) orantiseptic material to sanitize the waste materials as they aredeposited. Liner (54) includes support members (58) which may be conicalor any suitable shape to support the cage insert between itsperforations. The assembly of cage insert and bottom liner is encased ina folded waste bag (56) which can be enfolded around both the insert andthe liner and removed to clean the cage. The entire bag and assembly canthen be sealed and discarded to minimize the exposure of attendants toallergens or other harmful agents generated by the resident animals. Thewaste bag can be made of any suitable non-porous flexible polymericmaterial, such as polyethylene.

[0110] Preferably, bedding/nesting material (60) is placed on top ofcage insert (52) as shown in FIG. 4 so that the resident animals canform nests, burrow and play with the materials. The bedding is formed ofnon-toxic polymeric materials such as nylon. Although not shown, otherenrichment or play materials can be placed in the cages such as smallboxes of various shapes and sizes, posts, ladders, treadmills andhammocks.

[0111] Flange (8) on base (4) protects the seal with the top (6). Asshown in detail in FIG. 7, a gasket (62) is fitted over the edge of top(6) and fits snugly into the recess of flange (8) of the base. Thegasket can be made of any suitable elastomeric sealing material, and caneasily be made by splitting flexible tubing. FIG. 8 illustrates analternate embodiment in which gasket (62) is applied over a straightedge of base (4) and the gasket is covered by a flange (8) on the top(6).

[0112] The cages of the invention can be used individually forisolation, containment and/or transport of a variety of organisms inresearch, breeding, housing, storage and shipping. The sizes andproportions of the isolation containers can be selected according to theneeds of the organisms and/or specimens. Where significant numbers oflaboratory animals are to be maintained, the cages are preferablyintegrated into a cage rack system such as illustrated in FIG. 20, withmultiple cages mounted on supports (70) or (84) on at least one side ofa vertical support wall (74). Suitable lighting, controlled by a timer,can be incorporated in the wall (not shown here). The cages are arrangedwith the front (intake) ends outward, so that the exhaust air flowingfrom the other ends tends to flow vertically upward along the supportwall. Exhaust nozzles (25) (not shown here) can be attached to anexhaust duct system leading directly to the room, building HVAC system,or outside. Any suitable means of such mounting of the cages in verticalarrays can be used, but preferred shelfless support systems areillustrated in FIGS. 14 to 19. These support systems are simpler thanshelves, provide better visibility of the resident animals, and byproviding more uniform environmental conditions in the cages, result inless variability of the lab animals.

[0113] The end cage support bracket (70) of FIG. 14 is fastened tosupport wall (74) by bolting flange (75) to the support wall with screwsor bolts (72) or other suitable fasteners. The support wall ispreferably made of stainless steel or similar inert, nonporous material.The bracket has a vertical member (73) and a horizontal member (71)which serve to support the outer corner edge of the cage at the end of arow, and stop (76) which positions the cage laterally along the bracket.Such end brackets are used at each end of all rows of cages. Latchpiece(78) is swivel-mounted by screw (82) or other suitable swivel means.Handle (80) is provided for user convenience, and a similar piece, latchstop (81), inside the latchpiece limits the travel of the latchpiecebeyond the horizontal or vertical positions.

[0114]FIG. 15 illustrates middle brackets (84) which simultaneouslysupport two cages, being used to support all but the endmost cages ineach row. The brackets are fastened to support wall (74) by flanges (75)with screws (72). The brackets have vertical member (73) and horizontalmembers (71) which support the corner edges of the two adjacent cages ineach row. Stops (76) are provided on each horizontal member to positionthe cages. Latchpiece (86) is mounted by swivel screw (82) and spring(83). Spring (83) fits inside the hole in the latchpiece, with screw(82) passing inside the coil spring. The latchpiece is thus maintainedin any set position by the tension of the spring, which can be overcomeby slight pressure when the latchpiece is to be rotated. The outer edgesof latchpiece (86) are bent outward to provide convenient handles forthe attendant.

[0115]FIGS. 16 and 17 illustrate alternative means of mounting the endand middle support brackets to support wall (74) by employing hooks ortabs (88) which fit into spaced slots (90) in the support wall (74). Theslots could also be included in vertical support pieces (not shown)which are fastened to the support wall. Such slotted vertical supportpieces and hooked shelf brackets are commercially available.

[0116]FIGS. 18 and 19 illustrate the operation of the swivelinglatchpieces on the middle and end brackets, respectively. Whenlatchpiece (86) is positioned horizontally on middle bracket (84), itprevents the two adjacent cages which are partially supported by thatbracket from being slid out of position. When the latchpiece is swiveledto the vertical position as shown at (79), either or both cages can beremoved, provided that the latchpieces on the other sides of the twocages are also swiveled to the vertical position. Similarly, whenlatchpiece (70) of the end bracket is positioned horizontally, the cageis retained in position, but when swiveled to the vertical position asshown at (77), the cage can be removed, provided that the latchpiece onthe middle bracket on the other side of the cage is also placed in thevertical position.

[0117]FIG. 20 illustrates one cage (2) of a bank mounted on two middlebrackets (84). The cage can be mounted between the two middle bracketsand supported by the flanges on the cage base. Support wall (74) issupported by beam (92) or other suitable means, and the beam issupported by frame (94) which is shaped to prevent the cages fromcontacting adjacent walls of the room. All rack components are designedto be free of sharp edges or projections, with minimum ledges, angles,corners and overlapping surfaces to minimize the accumulation of dirt,debris and moisture. This facilitates effective cleaning anddisinfecting, providing safe working conditions. Preferably the racksystem includes caster wheels (96) to facilitate moving and positioning.At least two of the caster wheels should have brakes (not shown).

[0118] This unique shelf-less cage support design reduces experimentalvariability between animals and improves their visibility in the cages.Accessibility of the cages, illumination in the cages and theventilation system are also all improved. The shelf-less configurationprevents the accumulation of moisture and heat loads under shelves,while promoting upward air currents and air stratification against thesmooth surface of the support wall. The simple cage-lock system ensuresexact placement of each cage on its support brackets at optimal distancefrom the support wall.

[0119] Due to the natural upward convection flow of air created in thecages by the heat generated by the resident animals, mechanicalventilation is not required for the cages of the invention, whethermaintained individually or in banks as described above. Attachingexhaust nozzles (25) to the exhaust vents can improve the laminar flowof air. Such exhaust nozzles can be any shape suitable to channel airfrom the rectangular exhaust port to a round outlet or connection.Preferably, the nozzle is shaped or “tuned” to provide unobstructedlaminar flow from the exhaust port. If required, the exhaust nozzles ofcages maintained on the shelfless rack systems described above can beconnected to a mechanical exhaust ventilation system incorporated intothe support wall (not shown here). Such an exhaust system is illustratedin advertising for the GENTLEAIR (™) ventilated rack system produced byAlternative Design Manufacturing & Supply, Inc. of Siloam Springs, Ark.,which is incorporated herein by reference.

[0120] The advantages of the invention are illustrated by FIG. 21, whichshows a computer-simulated laminar convection flow of air (A) fromintake to exhaust ports in a cage (2) not containing a feeder structure.This two-dimensional longitudinal cross-section analysis of a mouse cageof appropriate height represents the worst case scenario when five mice(not shown) are located near the air inlet. The airflow through the cageis driven by the thermal currents generated by the mice. There is someturbulence created, but the airflow remains appropriately laminar. Ifthe animals are located at other sites such as in the middle when theyare eating or at the opposite (exhaust) end when they are exercising orsleeping, the air flow becomes uniformly laminar across the cage. Theairflow is driven upward and toward the exhaust because of the upwardthermal air currents from the animals and the sloping dome-shapedceiling of the cage. Computational modeling indicates that refill ratesof 15 times per hour can be accomplished with 1.5 square inches offilter material at each end, with a resistance of 0.5 inch of water at360 cubic feet per minute per square foot.

[0121]FIG. 22 illustrates the laminar convection flow of air (A) throughthe cage (2) containing the feeder, other accessories and resident mice.The mice (not shown) are located near the feeder in the middle of thecage. It can be seen that the support tubes for the feeder help toincrease air flow across the floor of the cage. No drafts appear toresult from the presence of the feeder structure.

[0122] In contrast, FIG. 23 is a similar computer-modeled airflow for amouse cage (95) of a similar size, but having the “Petri dish” form andhaving only filter material at the top (97). A group of mice (102) ishuddled under feed rack (100). It can be seen that considerableturbulent convection flow results, as shown by (B), with dead air areas(C) which will tend to produce unhealthy conditions for the animals. Theonly air intake is from the filter top, and there is no real airexchange with the outside. Notably, there is no escape of air exceptaround the lid (97), which is rather inefficient. The model shown is fora free-standing box; the air circulation pattern for such boxes arrangedin typical banks on shelves would be much worse.

[0123] For small rodent cages, the presently preferred configurationincludes a base and removable top with intake and exhaust ports locatedat the bottom and top of the cage, respectively, and on opposite ends.The animals can be inserted or removed by removing the top of the cage.For larger laboratory animals, alternate means of access and egresswould be considered. For example, FIG. 24 shows an end view of a cage(200) with an access door (202) included in the base (206) above theintake port (208), and FIG. 25 shows an end view of a similar cage (210)in which the access door (212) includes the intake port (214). FIG. 26is a side view of a cage (220) in which an access door (222) is includedin the side of the top (224). If desired, larger cages can use aone-piece construction, with intake and exhaust ports at either end andan access door occupying a substantial portion of the side of the cage(not shown).

[0124] Turning now to additional FIGS. 27 to 33 which illustrateimproved or alternative embodiments of the present invention, FIGS. 27to 29 illustrate certain features of an alternate embodiment of the cageof the invention. The assembled cage 240 includes a base portion 242which is made primarily of a transparent material such as apolycarbonate plastic. Optionally, corner and edge portions such as 244can be made of thicker portions of the same material for strength, withthe result that these portions are translucent rather than transparent.Intake port 252 is preferably fitted with a filter or screen 254. Asliding waste tray 274 is fitted under the bottom of the base portion242 to catch waste passing through the perforations in the perforatedcage insert 270, which is retained in place by suitable mechanical means(not shown here). Notches 250 are cut into the bottom edge 248 of baseportion 242 to retain the cage upon shelfless supports, discussed below.

[0125] The cage is shown as occupied by one mouse 268. Sipper tube 272is visible through the front wall of the cage. Perforated support 266 isalso visible, and takes the form of an inverted half tube with a shallowdepression at the top where the V-shaped feeder rests, allowing thissurface to serve as a feed tray. Perforations 279 are provided insupport 266 for visibility and ventilation, and support 266 preferablyis made of non-toxic material such as nylon or stainless steel. Top 246is sealingly attached to the base portion and secured with a clip 258resting in notches 256 in the top edge of the top 246. The top and baseare preferably designed so that they join to form an air-tight seal. Theunderside of the top 246 forms a sloping domed ceiling (not visiblehere) which slopes upward from the front (intake) end to the rear(exhaust) end, as in the embodiment described and illustrated above.

[0126] Water bottle 260 is visible in FIG. 27, and illustrated in detailin FIG. 29. Neck 286 is inserted into aperture 289 of resilient fixture288, allowing water to run into sipper tube 272. The bottle can be anysuitable container which can be fitted into the allowed space on thetop, but is preferably a standard commercial bottle such as an “Odwalla”juice bottle, marketed in 4 oz., 8 oz. and 16 oz. sizes, for convenienceand economy. Feeder lid 262 covers a space for a drop-in portion of thefeeder structure . It is hinged by pin 269 to connections 247, withhinge plate 264 connecting to lid 262. Tab 267 can be used for liftingthe lid by finger or hand tools. V-shaped feeder rack 290 has slots 292to allow food access to the occupants, and is similar to the structuredescribed-above. V-shaped feeder 290 is inserted through opening 263when lid 262 is raised, and rests upon the upper surface 277 ofperforated support 266. Perforated support 266 is solid and recessed onthe top, except for sills 276 which close off both ends to form ashallow depression or tub-like area 277. This area serves not only tosupport the V-shaped rack but to hold powdered feed, feed fragments, oreven liquid or viscous feed.

[0127] Sliding waste tray 274 is retained in place below perforated cageinsert 270 by lip 296, and can be removed using tab 294. Cage floorinsert 270 is retained in the cage base by rim 298. Exhaust port 278 ispreferably fitted with a screen or filter 280, and optionally with anexhaust nozzle 282, which is retained in place by rim 284. As discussedabove, exhaust nozzle 282 can be used as is, or connected to manifoldmeans to direct exhausted air to another area or a ventilation system.Both the intake and exhaust ports in this embodiment are oval, or couldbe round.

[0128] The features discussed above are shown in further detail insectional views 30 and 31, particularly portions of the feeder and waterdelivery systems. For example, FIGS. 30 and 31 show depression 277 andsill 276 more clearly. The sloping domed ceiling 299 of the cage isshown in FIG. 30. Absorbent material 320 is placed in waste tray 274 tohandle waste, as discussed above for the first embodiment. The cages aresupported in position by support bars 306, part of the shelfless rack.The other features shown in FIGS. 30 and 31 are described above withreference to the same numerals in FIGS. 27-29.

[0129]FIGS. 32 and 33 illustrate an array of cages 240 in place on cagerack 300. The rack includes uprights 302, vertical support wall 304,lateral supports 307 and horizontal support bars 306, which physicallysupport the cages. It can be seen that this provides a shelfless racksystem equivalent to that described above for the first embodiment.Support wall 302 forms a space in which an exhaust chimney 316 isprovided for each vertical array of cages. Exhaust chimneys 316 can takeup half the thickness of support wall 304 as shown in FIG. 33, or canextend to the full thickness of the wall. Exhaust chimneys 316 areformed to have a wider cross section at the top than at the bottom toaid convective air flow of the exhaust, and are separated by voids 322.The exhaust nozzles 282 of cages 240 are attached to exhaust connections308, thus entering exhaust chimneys 316. Thus, when the cages are inplace, air enters the intake ports at the exposed (front) ends of thecages, passes through the cages in laminar convective flow, and isexhausted through the exhaust ports 278 and exhaust nozzles 282 intoexhaust chimney 316. The exhausted air rises upward (as indicated byarrows) due to its elevated temperature and convective effects, isgathered by manifold 312 and passes into exhaust stack 314. As discussedabove, this exhaust can simply be directed to the outside air or can beconnected to a mechanical exhaust or ventilation system. As describedabove, wheeled casters 310 are provided for mobility.

[0130] At the top of support wall 304 where it joins manifold 312, alamp 318 is installed to provide light to the cages when desired. Anysuitable fluorescent or incandescent lamp can be used, including fullspectrum lamps which simulate sunlight. The light is transmitted downthe exhaust chimneys 316 via their mirrored interior surfaces 324, andenters the cages via the exhaust nozzles 282 and exhaust ports 278. Thereflective surface of domed ceiling 299 facilitates the flow of gases.

Selection and Manufacture of Filter Media

[0131] Depending upon the needs of the animals and the characteristicsof the environment, a wide variety of filter media can be used in theintake and exhaust ports of the cages. Preferably, the filter media willexclude contaminants larger than about one micron, more preferablycontaminants larger than about 0.5 micron, and most preferably,contaminants larger than about 0.1 micron. In most cases, the filtermedia will be ordinary mechanical filters. Flat or panel mechanicalfilters generally consist either of a low packing density of coarseglass fibers, animal hair, vegetable fibers or synthetic fibers, oftencoated with a viscous substance (e.g., oil) to act as an adhesive forparticulate material, or even slit and expanded aluminum. Flat filterscan efficiently collect large particles, but remove only a smallpercentage of the smaller particles which are respirable by humans. Flatfilters may also be made of “electric” media, consisting of apermanently-charged plastic film or fiber. Particles in the air areattracted to the charged material.

[0132] Pleated or extended surface filters generally attain greaterefficiency for capture of respirable size particles than flat filters.Their greater surface area allows the use of smaller fibers and anincrease in packing density of the filter without a large drop in airflow rate. (In each case, there are tradeoffs between filteringefficiency and air flow to be considered.) High Efficiency ParticulateAir (HEPA) filters can be used, and are described below. The intake andexhaust filters will of course be changed periodically, according toconditions.

[0133] Preferably, the filter medium is a gas-permeable filter membranecapable of capturing all particles above a certain minimum size (e.g.,one micron) while allowing air and other gases to pass freely. Suitablemembranes can be prepared, e.g., as disclosed in U.S. Pat. No.5,190,879, which is incorporated herein in its entirety by reference.The 0.1 micrometer to 0.3 micrometer grade of material presents aneffective barrier to microbes and particulate matter, with titerreductions at an efficiency of ten million.

[0134] Other suitable membranes include the flexible air permeablenon-woven fabric filters of U.S. Pat. No. 4,540,625 (expired) and thefilter material comprising porous apatite particles embedded in watersoluble glucan of U.S. Pat. No. 5,143,752. Both of these patents areincorporated herein by reference in their entirety. Suitable filtermembranes are available commercially, e.g., from DuPont and PallFiltration.

[0135] Preferably the membranes are ultra-thin dense composite membranescomprising non-woven materials, which can be sterilized by exposure togamma radiation, ethylene oxide or autoclaving. The membrane creates apassive barrier to the movement of airborne contaminants into or out ofthe cage, while permitting the exchange of respiratory and toxic gases,carbon dioxide, ammonia, sulfuric waste by-products, microbes as smallas 0.1 micron in size and allergens.

[0136] The strategically placed intake and exhaust ports in the cages ofthe invention ensure high intracage airflow rates. The room-coupledstatic environmental closed system with improved air exchange isequipped with an exhaust port in the upper portion of the dome-shapedsloping top. The filter membrane therein effectively extracts cageeffluent through the low resistance membrane filtration system beforethe air re-enters the animal room. The membrane-filtration system in thebase of the cage is exposed to cool room air to optimize passive airdiffusion into the cage. Typically, in an animal room set at 66 deg. F.,50 percent relative humidity and fifteen air changes per hour, five micein a cage would generate 2.0265 Kcal/hr of heat, 0.5 g/hr of moisture,0.76 g/hr of carbon dioxide and 0.0016 g/hr of ammonia. With relativelylow air diffusion in the cage, the animals' thermal load and productionof moisture and gases produces upward movement of air and vapors,creating pressure differentials between the inside and outside of thecage toward the filtered passive exhaust system. The caging system thusmaximizes cage ventilation while minimizing the accumulation of heat andmoisture and eliminating the buildup of ammonia and other contaminants.More importantly, it provides “good air quality” for both animals andworkers. Good air quality can be defined as the absence of any substancein the air which is a health hazard or source of discomfort to theanimals or a threat to occupational health. Some common pollutantsinclude aldehydes, volatile organic compounds, sulfur compounds,ammonia, carbon dioxide, carbon monoxide, metabolic by-products,excessive moisture, dirt particles and allergens.

[0137] The natural convection created by the body heat of the animals inthe closed-system isolation enclosure drives the low velocity airfiltration. The use of laminar convection flow to ventilate themicroenvironment through the filter membranes serves to eliminate thebuildup of harmful gases and provide good air quality within theenclosure.

[0138] The particle retention of filter membranes in air is veryefficient. In air filtration, retention of particles is mostly by directinterception (mechanical capture of a particle by the filter) by thefilter matrix, but there are four additional factors which can causeparticles to be captured by the filter. These include: 1) inertialimpaction (the particles's inertia carries it in a straight line evenwhen the airstream bends), 2) gravitational settling (gravitationalforces may affect particles in an air stream), 3) electrostaticattraction (electrical forces create charge differences between thefilter and the particle, resulting in particle capture, and 4) Brownianmotion (very small particles exhibit the erratic movements of Brownianmotion). Because of their irregular flow paths, such particles are morelikely to be captured by the filter.

[0139] Various methods can be used to test filters. The “weightarrestance” test, described in the American Society of Heating,Refrigeration and Air Conditioning (ASHRAE) Standard 52-76, is generallyused to evaluate low efficiency filters, designed to remove the largestand heaviest particles. Such filters are commonly used in residentialfurnaces and the like. For the test, a standard synthetic dust is fedinto the air cleaner and the proportion (by weight) of the dust trappedon the filter is determined. Because the particles in the standard dustare relatively large, the weight arrestance test is of limited value inassessing the removal of smaller, respirable-size particles from indoorair.

[0140] The “atmospheric dust spot test”, also described in ASHRAEStandard 52-76, is usually used to rate medium efficiency air cleaners(both filters and electronic air cleaners). The removal rate is based onthe cleaner's ability to reduce soiling of a clean paper target, anability dependent on the cleaner removing very fine particles from theair.

[0141] Military Standard 282(3) [i.e., the percentage removal of 0.3micrometer particles of dioctylphthalate (DOP)] is used to rate highefficiency air filters, those with efficiencies above about 98 percent.High efficiency particulate air (HEPA) filters are commonly encounteredin the marketplace, and are a subset of high efficiency filters. Theyare typically rated using the DOP method. One standard-settingorganization defines a HEPA filter as having a minimum particlecollection efficiency of 99.97 percent by this testing method.

EXAMPLES

[0142] The invention will be further illustrated by the followingnon-limiting examples.

[0143] Computational Fluid Dynamics: Applicant recognized that acomprehensive study of air movement, heat transfer, and contaminationdispersal in the microenvironment of an animal cage could only beundertaken using computational fluid dynamics (CFD). CFD is athree-dimensional mathematical technique of numerical algorithms used tocompute the motion of air, water, or any other gas or liquid. Applicantused computer modeling software (NISA/2D and FLUENT/3D) to optimize thecage design and geometric parameters of a closed-system. CFD uses fiveNavier-Stokes equations for viscous fluid flows. They are energy, threemomentums, and mass conservation equations. The source (variablequantity, e.g. source of heat) solved transient (variable variation withtime) plus convection (variable transportation by motion of fluid) minusdiffusion (variable spread by gradient). Grid cells for which individualcalculations are made, consist of the boundary (plane applied to thegoverning equations) under study. CFD would agree to simulate differentconfigurations knowing that all conditions, except those being varied,remain constant (Memarzadeh, 1998). This makes comparisons of CFDsimulations actually much more reliable than comparisons of experimentalstudies, for which there are variables. Inputs for the CFD, such as heatdissipation at 2.3 watts, surface temperature at 30° C., moisture at 0.5g. H₂O per hr., CO₂ at 0.76 g. per hr. ppm, and NH₃ at 0.0016 g. per hr.generation rates for 5-mice model, were defined by a set of experimentalmeasurements in a wind tunnel (Riskowski et al., 1996).

[0144] Then, applicant created computer simulations and analyzed theventilation performance of different cage designs by computational fluiddynamics. Agreement with prior CFD analysis was maintained by usingcomputer software modeling NISA/2D analysis (Engineering MechanicsResearch Corp., Groton, Conn.) when comparing static microisolator cageswith filter tops and vented microisolation containers with closed tops.A series of cage configurations were developed which were examined byusing NISA/3D. Applicant further optimized the cage design by importinga Pro-E (Parametric Technology, Cambridge, Mass.) furniture design intothe more sophisticated computer software modeling FLUENT 4.5 (FLUENT,Inc., Lebanon, N.H.). The aim was to create a micro isolation containerwith adequate and filtered ventilation. The energy-efficient design forappropriate caging would lie within the animals; their metabolic heatthat rises towards the top and exits a filtered vent located at thehighest end of the cage, i.e. convective heat transfer. Subsequentdesign refinements would be based on the findings of this analysis.

[0145] Case Studies: The analysis of the flow processes in the cagefalls under the rubric of convective heat transfer (Bejan, A., 1984). Inthis case, the driving potential for the flow is the metabolic heatgenerated by the mice. The metabolic heat source creates a localizedbuoyant flow in which the heated air rises towards the top of the cageand exits the vent located at the highest end (rear) of the cage.Conservation of mass then requires that cooler air must enter the cagethrough the inlet located near the bottom at the front of the cage. Wemay gain some insight as to the magnitude of the various effects byconsidering a simple steady state model of the system. A steady statemodel implies that the mice remain stationary and that their metabolicrates remain stationary for a duration of time sufficient for the systemto reach a steady state. We may use the first law of thermodynamics towrite an energy balance for this simple model in which the air speed andtemperature at the inlet and exhaust are related to the metabolic heatsource:

{dot over (m)}C _(p)(T _(exit) T _(inlet))={dot over (Q)} _(metabolic)

[0146] Here {dot over (m)} is the mass flow rate of air entering andexiting the cage and C_(p) is the specific heat of the air.

[0147] The mass flow rate is related to the air speed by therelationship

{dot over (m)}=ρνA,

[0148] where ρ is the density of air , ν is the gas speed (velocity) andA is the cross sectional area of the inlet and exhaust sections of thecage. The unknown parameters in this model are the air speed and thetemperature difference between the inlet and exhaust. We may gain someinsight by manipulating the above equations into the form:${v\quad \Delta \quad T} = \frac{Q_{metabolic}}{\rho \quad {AC}_{p}}$

[0149] where ΔT=T_(exit)−T_(inlet). Inspection of this expressionindicates that for fixed ρAC_(p) an increase in the metabolic heatsource ({dot over (Q)}_(metabolic)) results in an increase in νΔT . Thisincrease indicates that either the exit temperature increases or the airvelocity increases or both increase. While this simple model does notprovide a predictive capability (since we may only solve for the productof gas velocity multiplied by the temperature difference) it doesprovide a simple interpretation of the flow process as well as a quickcheck of the validity of the numerical results which follow. In order toprovide a predictive capability we must solve the equations governingconvective heat transfer for the air in the interior of the cage. Theseequations are the conservation of mass, momentum and energy and areexpressed as a set of partial differential equations (Bejan, A., 1984):${\frac{\partial\rho}{\partial t} + {\nabla{\cdot \left( {p\overset{\rightharpoonup}{v}} \right)}}} = 0$${\frac{{\partial\rho}\overset{\rightharpoonup}{v}}{\partial t} + {\nabla{\cdot \left( {p\overset{\rightharpoonup}{v}\overset{\rightharpoonup}{v}} \right)}}} = {{- {\nabla P}} + {\nabla{\cdot T^{v}}} + {\rho \overset{\rightharpoonup}{g}}}$${\frac{\partial{\rho \left( {e + {\frac{1}{2}{\overset{\rightharpoonup}{v} \cdot \overset{\rightharpoonup}{v}}}} \right)}}{\partial t} + {\nabla{\cdot \left( {\rho \quad {\overset{\rightharpoonup}{v}\left( {e + {\frac{1}{2}{\overset{\rightharpoonup}{v} \cdot \overset{\rightharpoonup}{v}}}} \right)}} \right)}}} = {{\nabla{\cdot T^{v} \cdot \overset{\rightharpoonup}{v}}} + {{\nabla{\cdot P}}\overset{\rightharpoonup}{v}} - {\nabla{\cdot \overset{\rightharpoonup}{q}}} + {\rho \quad {\overset{\rightharpoonup}{g} \cdot \overset{\rightharpoonup}{v}}}}$

[0150] Here, {right arrow over (ν)} is the velocity, P is the pressure ,e is the internal energy, {right arrow over (q)} the heat flux and T^(ν)the viscous stress tensor and T is the temperature.

[0151] We also need constitutive equations for the internal energy,density, heat flux and viscous stress:$T^{v} = {{{- \frac{2}{3}}\mu {\nabla{\cdot \overset{\rightharpoonup}{v}}}I} + {\mu \left( {{\nabla\overset{\rightharpoonup}{v}} + \left( {\nabla\overset{\rightharpoonup}{v}} \right)^{T}} \right)}}$

[0152] The equations represent severe mathematical difficulties andgenerally must be solved using computational techniques. The simulationresults presented in this application were obtained using the commercialpackage FLUENT-UNS. The flow within the cage likely experiencesturbulence, thus a turbulence model is required. The turbulence modelused in this work is the Renormalization Group (RNG) k-ε model (Yakhotand Orszag, 1986). In addition, we model the buoyancy effect byincorporating the Boussinesq approximation (Bejan, A., 1984). Solutionof the above set of equations and approximations provides a detailedpicture of all of the flow variables ( pressure, temperature, velocity)for the air in the cage. We again consider the cage to be in a steadystate condition.

[0153] Recent advances in solid modelling technology enable the analystto easily create computational meshes that embody the importantgeometric characteristics of a given physical situation. The solid modelin this work represents the volume occupied by the air and the model wascreated and meshed with the commercial solid modeling software packagePro-E (Parametric Technology, Cambridge, Mass.) Simulation results arepresented for seven cases described below, using computational gridsmade up of 115,210 tetrahedral cells with 23,340 nodes at the corners ofthe cells. The meshed model is imported into FLUENT-UNS for analysis.The heat source modeling the mice is placed under the feeder, below theinlet and below the exhaust and in the corner in these simulations.Also, examined were contours of static temperature, velocity vectors,particle traces by residence time, and entrainment of the ammonia in theflow.

[0154] Once the CFD phase was completed and final design and geometricparameters of the closed-system cage were optimized, a full-size cageprototype was constructed with dimensions of 7.25×11.5×7.2 in. Also,used was a 5-mice electric circuit model to simulate body heat loads(2.3 watts equivalent to 2.0265 Kcal/hr) from five mice in the prototypecage The cage was equipped with all the caging system furniture such asfeeder, sipper tube and a waste disposal system that consists of a wastetray liner, perforated floor, and nesting material. Although no animalswere housed within the cage, watering and feeding devices weremaintained filled. The cage was tested in a room or wind tunnel set at72° F. and 50 percent relative humidity in still air. Applicantperformed qualitative and quantitative analyses of air distributionpatterns, velocity, air change per hour, and leakage. Hot filmanemometry and smoke tests were used to correlate CFD predictions andoptimize airflow inlet and exhaust.

[0155] Air Velocity determination: Air velocity was measured at theinlet of the cage, using hot film anemometry. To measure inlet flowvelocities of this magnitude (less than 10 cm/s) via hot film anemometertechniques it is important that the direction of both free and forcedconvection from the hot film be the same (i.e., vertically upward). Toaccommodate this a right angled downward pointing adapter with acircular inlet was placed over the cage inlet. The hot film was placedat the center of the adapter tube entrance. The velocity at the cageinlet was calculated from the measured velocity at the adapter'sentrance and the tube/cage inlet area ratio of 83 percent. The hot filmwas calibrated via a vertically orientated laminar flow tube (with aparabolic velocity profile) and a massflow controller to regulate theair flow. Air flow velocities were measured at the inlet for severalinlet/outlet filter types via hot film anemometry. Attempts to measurethe exhaust flow rate via soap bubble techniques were performed. Anothertechnique used high speed video recordings of smoke flowing at theexhaust against a background grid in the plane of light. The smoke wasintroduced directly in the occupied cage by dropping smoke matches atthe inlet. The cage was occupied by five outbred mice weighing 24 gramson average. Intracage air velocity was estimated by smoke observation.

[0156] ACH rate determination: Intracage air exchange rates wereestablished by determining the velocity (U), area (A), flow rate (Q),and volume (V). The total volume of air change per hour or continuityequation solves for the following.${Q\left( {{cm}^{3}\text{/}s} \right)} = {{{U\left( {{cm}\text{/}s} \right)} \times {A\left( {in}^{2} \right)} \times (2.54)^{2}{ACH}} = \frac{3600 \times Q}{V({ml})}}$

[0157] Air Distribution: Intracage air distribution pattern wasdetermined by visually observing smoke dispersion patterns afterintracage release in the prototype. Smoke was released from a titaniumtetrachloride (TiCl₄) smoke stick (Model 15-049, Liberty Industries,Inc., East Berlin, Conn.) inside the cage at a point on a centerlinebetween the cage front and back, intermediate between the cage floor andthe bottom of the top in the middle of the cage. Smoke was observeduntil it was no longer visible. Video records of air flow patterns, atthe inlet, at the outlet and inside the cage, were obtained by laserlight sheet illumination of smoke introduced at the inlet. The laserlight sheet for illuminating the smoke was delivered via a 6 watt Argonlaser, a fiber optic cable, focusing lenses and a light sheet producingcylindrical lens. The removable top of the mouse cage was replaced witha glass plate for the visual tests. The light sheet was projectedvertically down through this glass plate, illuminating only a slice ofthe cage's volume from the inlet to the outlet. Video tapes recorded theflow field in the illuminated slice. Leakage rate determination: Airleakage from the cage was determined qualitatively by visualizing smokeescaping from the cage. Leakage was observed from the junction of thecage top and bottom and along the front of the cage. Leakage wasexpressed qualitatively as present or absent. In addition, leakage wasvisualized after intracage smoke release from a TiCl₄ smoke stick.

Results

[0158] CFD simulation results with and without the feeder-troughassemply in place are as follow:

[0159] Case 1—No Feeder-Trough Assembly. 5-mice model located at centerof cage.

[0160] Case 2—No Feeder-Trough Assembly. 5-mice model located at centerof outlet.

[0161] Case 3—No Feeder-Trough Assembly. 5-mice model located at centerof inlet.

[0162] Case 4—No Feeder-Trough Assembly. 5-mice model located at cornerof outlet.

[0163] Case 5—With Feeder-Trough Assembly. 5-mice model located atcenter of cage.

[0164] Case 6—With Feeder-Trough Assembly. 5-mice model located atcenter of outlet.

[0165] Case 7—With Feeder-Trough Assembly. 5-mice model located atcenter of inlet.

[0166] Total Gas volume in cage=8.9×10⁻³ m³

[0167] Inlet Temperature=20.0 C. Case 1 2 3 4 5 6 7 Å (m³) 9.7 × 10⁻³9.7 × 10⁻³ 9.7 × 10⁻³ 9.7 × 10⁻³ 9.0 × 10⁻³ 8.9 × 10⁻³ 8.9 × 10⁻³ T_(e)(C) 27.45 26.45 27.70 27.85 27.65 25.65 27.45$v\left( \frac{cm}{\sec} \right)$

12.4 9.9 11.9 11.1 11.5 9.6 12.2$\overset{.}{\forall}\left( \frac{{cm}^{3}}{\sec} \right)$

260 270 240 260 240 270 240 ACH 96.5 100.2 89.1 96.5 96.0 109.2 97.1

[0168] CFD simulations of contours of static temperature, velocityvectors, particle traces by residence time, and entrainment of theammonia in the flow revealed constant airflow distribution in the cage.Computer simulation illustrated the effects of inlet and exhaustvariances on the air exchange rates.

[0169] Applicant used CFD to optimize and simulate the effects of inletand exhaust opening variances on the air exchange rates. Computersimulations demonstrated the existence of adequate air changes withoutdrafts, metabolic contaminant buildup, or the need for mechanicalventilation while still providing effective barriers to protect thehealth of the animals and personnel. The environmentally-enrichedcage/rack closed-system uses filtered ventilation by convection airflowto provide adequate air changes per hour without drafts, metaboliccontaminant buildup, or the need of mechanical ventilation whilesafeguarding animal and occupational health and well being.

[0170] The CFD simulation results of contours of static temperature withthe 5-mice model near the exhaust revealed a temperature gradient of5.75° C. between the inlet and the exhaust. This is the energy necessaryto induce convective heat transfer, buoyant flow and conservation ofmass. The contours observed illustrated the heat rising, with the airbeing hotter toward the top. The feeder-trough assembly obstructs,diverts, and redistributes the airflow from the inlet such as it coolsthe air by 1.7° C.

[0171] The CFD simulation results of velocity vectors with the 5-micemodel near the exhaust revealed airflow of 9.6 cm/s from the inlet tothe exhaust. This is the result of thermodynamics: convective heattransfer, buoyant flow and conservation of mass. The observed velocityvectors illustrated the even air distribution pattern at the animallevel, with the air moving sideways and toward the top. The feederassembly obstructs and diverts the airflow from the inlet such as it isslowing and redistributing the air at the bottom of the cage, making itmore comfortable at the animal level.

[0172] The CFD simulation results of particle traces by residencetime(s) with the 5-mice model near the exhaust revealed that 67 percentof airborne contaminants exit at the exhaust in approximately 23seconds. This is an effect of thermodynamics: convective heat transfer,buoyant flow and conservation of mass. The particle traces observedillustrated an even air distribution pattern at the animal level, withthe air moving sideways and toward the top. The majority of particlecontaminants exit at the exhaust, with the remaining (33 percent)trapped near the ceiling. Heavier particle contaminants move sidewaysand get trapped under the floor. The feeder-trough assembly obstructsand diverts the airflow from the inlet such as it is cleaning the air atthe bottom of the cage, making it more comfortable at the animal level.

[0173] The CFD simulation results of the entrainment of the ammoniagenerated at floor level with the 5-mice model near the exhaust revealthat ammonia exhausts the cage at 59 percent through the vent located atthe highest end of the cage. This is the result of thermodynamics:convective heat transfer, buoyant flow and conservation of mass. Thefeeder-trough assembly obstructs and diverts the airflow from the inletso that the remaining 41 percent of ammonia moves sideways and below theperforated floor, making it more comfortable at the animal level.

[0174] Three-dimensional (3D) FLUENT velocity vectors and velocity plotsdiagrams were developed with the feeder in place (not shown). Bothsloped-ceiling and feeder were represented by step-like structures,while the air inlet and exhaust were square-like structures. The 5-miceheat load was located in the back of the cage next to the feeder.Another diagram showed the 5-mice in a half-cage model, inducing acircular airflow pattern without turbulence. There was predominantlaminar airflow against the backside of the cage near the exhaust. Also,secondary laminar airflow existed right above the perforated floor,suggesting natural convection airflow. Another diagram illustratedvelocity plots induced by the 5-mice in a full-size cage model. Therewas a bottom flow next to the 5-mice residents in the cage. The airvelocity was maximal near the 5-mice and high at air inlet and exhaust.Waste gas (NH₃) and particulates (24 microns) behaviors under the sameboundary were examined using FLUENT/3D. Probably due to theirgravitational settling behaviors, there was a strong tendency for themto move under the perforated floor where they are being trapped. Basedon these analyses, one would expect low NH₃ concentrations, drymicroenvironment, and minimal contaminants, allergens and odorconcentrations in the cage right above the floor and out of the cage,thus assuring adequate ventilation, good air quality, and comfortableand healthy microenvironmental conditions.

[0175] Also, vector and velocity plot diagrams enabled examination ofairflow patterns associated with intracage obstructions and animal heatloads.

[0176] Applicant measured heat generation for a five mice huddlingequivalent (5-mice) under the same boundary conditions. This permittedapplicant to examine the effects of intracage convection air flowquantitatively and qualitatively, including air pressure, velocity anddiffusion patterns inside the cage. Furthermore, airflow dynamicsassociated with microenvironmental factors of ventilation, temperatureand humidity were examined. The results of computer modeling indicatethat the closed-system design of the invention is highly effective inmaintaining stable temperature, low humidity and adequate air exchange.The system employed a filter bank that has been designed to keep theexchange of pathogens and particulates between cage and housing room toa minimum while assuring clean air environment and adequate ventilation.

[0177] Tests of systems with no inlet and outlet filters produced an 8.3cm/s air flow velocity at the inlet centerline. With the assumption of auniform velocity profile across the inlet this would indicate an inletflow rate of 161 ccs (inlet area=outlet area=19.3 sq. cm). With theassumption of uniform mixing within the cage and a cage volume of 8250cc the calculated air exchanges per hour would be 70.14 ACH.

[0178] The second technique of the validation study was by hot filmanemometry conducted at Colorado State University (CSU), Fort Collins,Colo. The airflow velocity was calibrated by vertical laminar flow tubeand regulated by a mass flow controller. With air velocities of lessthan 10 cm/s, the technique fails to be accurate. However, the estimatedair velocities for the closed-top filter-cage are: 8.3 cm/s for 70 ACH(open vent), 6.5 cm/s for 55 ACH (wire cloths), and 1 cm/s for 8.45 ACH(filter membranes).

[0179] The laser light sheet visualization of smoke tests were performedunder the no inlet/outlet filter conditions only. These smoke flow testsdemonstrate that when the simulated mice are: 1) grouped near the inlet,the primary circulation is up from the inlet, along the sloped roof tothe outlet, 2) grouped under the outlet, the primary circulation is fromthe inlet along the ground to the mice and then up to the outlet. Aninternal secondary circulation cell is created in the portion of thecage not occupied by the primary circulation. The smoke tests indicatedthat the flow through the cage is somewhat influenced by room aircirculation patterns outside the cage. It is optimal to align the cagesuch that the room air flow is predominantly towards the cage inlet.

[0180] Tests with filters on the inlet and/or outlet essentially stoppedthe primary flow pattern (i.e., inlet to outlet) from forming andcreated only internal flows within the cage. A fine mesh stainless steelwire-cloth (150×150 mesh size) on the inlet and outlet produced small(less than 1 cm/s, not measurable with hot film techniques) inlet flowvelocities. When a wire-cloth of 40×40 mesh size was used on the inletand outlet, the inlet flow rate was approximately half of the unimpededflow values.

[0181] The third technique of the validation study is the smoke testconducted in a wind tunnel at CSU. Video records of airflow patterns atthe inlet, exhaust and inside the cage were obtained by laser lightsheet illumination of smoke released from titanium tetrachloride sticksat the inlet. A 6 watt Argon laser, fiber optic cable, and focusinglenses were used to illuminate only a slice of the cage volume, makingit easier to observe air distribution patterns.

[0182] With the 5-mice model located near the exhaust, the studyobserved the air rising towards the top and exiting through the ventlocated at the highest end of the cage. This too, is consistent withthermodynamic principles: convective heat transfer, buoyant flow, andconservation of mass.

[0183] Smoke distribution patterns and calculated air velocity rateswere visualized from real-time frame analysis. With the 5-mice modellocated near the inlet, the primary air circulation pattern moves upfrom the inlet and along the sloped roof to the exhaust, a top flow.With the 5-mice model located under the exhaust, the primary aircirculation pattern moves from the inlet along the floor to the 5-micemodel and then up to the exhaust, a bottom flow. The estimated airvelocities were: 7 cm/s for 59 ACH (open vent), 4.1 cm/s for 35 ACH(wire cloths), and 0.5 cm/s for 4 ACH(filter membranes).

[0184] Air leakage was visualized after smoke was released from smokesticks inside the cage. No leakage was observed from any components, inany configurations. It was observed that the flow through the cage isinfluenced by room-air circulation patterns outside the cage. It isoptimal to align the cage such that the room air flows towards the cageinlet.

[0185] It can be concluded that the thermodynamics of natural convectionwould remove metabolic heat, moisture, and gaseous contaminants andprovide good air quality. It can be used in a static closed-system cagefor producing adequate contaminants and provide good air quality. It canbe used in a static closed-system cage for producing adequatemicroenvironmental ventilation and efficient in/out biological barriersat cage level.

[0186] Although the present invention has been described with referenceto preferred embodiments, numerous modifications and variations can bemade and still the result will come within the scope of the invention.No limitation with respect to the specific embodiments disclosed hereinis intended or should be inferred.

I claim:
 1. An isolation container comprising: a base which supports aplurality of sides; a top affixed to the sides forming a microisolationcontainer suitable to house a heat load; one of said sides having anintake port with a filter membrane; a second of said sides having anexhaust port with a filter membrane; said exhaust port being locatedhigher relative to the base than the intake port on an opposite side,thereby facilitating a convection based air flow from the intake port,across the container, and out the exhaust port.
 2. The isolationcontainer of claim 1, wherein the plurality of sides comprises foursides forming a rectangle, the intake and exhaust ports are located atopposite ends on a pair of shorter sides, and the inner surface of saidtop slopes upward from the intake port side to the exhaust port side. 3.The isolation container of claim 2 wherein said top comprises a watersupply vessel terminating in a sipper tube within the container.
 4. Theisolation container of claim 3 wherein said water supply comprises awater bag constructed from flexible polymeric material.
 5. The isolationcontainer of claim 3 wherein said water supply comprises a bottle. 6.The isolation container of claim 1 wherein said base and said top can beassembled to form an airtight seal.
 7. The isolation container of claim1 which further comprises a feeder assembly designed to fit inside saidcontainer.
 8. The isolation container of claim 7 wherein said feederassembly comprises a V-shaped slotted rack for holding feed and aperforated support supporting same.
 9. The isolation container of claim8 wherein said feeder assembly is adapted to be inserted through anaperture in said top.
 10. The isolation container of claim 8 whereinsaid perforated support is made of non-toxic material.
 11. The isolationcontainer of claim 8 wherein said perforated support comprises twoperforated tubes.
 12. The isolation container of claim 8 wherein saidperforated support comprises a single half tube.
 13. The isolationcontainer of claim 2 wherein said base comprises a removable waste trayto facilitate cleaning of the container.
 14. The isolation container ofclaim 2 wherein said base comprises a floor assembly comprising aperforated cage floor insert, an absorbent cage bottom liner under saidcage insert, and a waste bag encasing said cage insert and said bottomliner for disposal.
 15. The isolation container of claim 2 wherein saidexhaust port has an external exhaust nozzle attached thereto.
 16. Theisolation container of claim 2 which is so configured as to providelaminar convective airflow between said intake port and said exhaustport when said container is occupied by at least one live animal.
 17. Asystem having a plurality of rectangular isolation containers arrayedupon a vertical support rack, comprising: a) a rack comprising a baseand a vertical support wall which comprises a shelfless cage support,and b) a plurality of microisolation containers, each mounted upon atleast one side of said vertical support wall by said shelfless support,said isolation containers comprising a base made of transparent materialand having an intake port covered with a filter at the front end thereofand a detachable top sealingly attached to said base, said containerhaving an exhaust port covered with a filter and located on the rear endof said container, opposite the front of said base, with the interior ofsaid top forming a domed sloping ceiling for said container, the lowerportion thereof being adjacent to the intake end and the upper portionbeing adjacent to the exhaust end, wherein each of said containers ismounted with its rear end adjacent said vertical support wall.
 18. Thecontainer-support system of claim 17 wherein each of said containerscomprise an external exhaust nozzle attached to said exhaust ports andeach of said exhaust nozzles are connected to an exhaust manifold toremove air exhausted from said containers.
 19. The container supportsystem of claim 17 wherein said base comprises a floor assemblycomprising a perforated cage floor insert, an absorbent cage bottomliner including means to support said cage insert, and a waste bagencasing said cage insert and said bottom liner for disposal.
 20. Arectangular microisolation container comprising a base made oftransparent material and having an intake port covered with a filter atthe front end and a detachable top sealingly attached to said base, saidtop having an exhaust port covered with a filter and located on the rearend of said top, opposite the front of said base, with the interior ofsaid top forming a domed sloping ceiling for said container, the lowerportion thereof being adjacent the air intake end and the upper portionbeing adjacent the air exhaust end.